Most people are familiar with horizontal axis wind machines. These include the charming Dutch and Danish water pumping machines, the smaller sail windmills of Portugal, Greece and other areas, the iconic multi-blade water pumpers of the American west (millions sold), and the ever larger and more expensive three-blade wind turbines being used around the world to generate electricity. Hundreds of different wind machine designs have been proposed, built and tested and innovation continues to this day.
The vertical axis wind machines are less well known. These had been invented and refined hundreds of years before the horizontal axis machines. Two ancient and classic designs are worth noting. The simplest is a brush/reed mesh vertical rotor with the wind focused by mud walls. These have been used for more than a thousand years.
The second kind is a much more complex, but adaptable, Chinese model with multiple vertical sails. The sails on a Chinese windmill can be furled, but scoops and blades on many vertical axis types can’t be turned out of the wind in a gale like a horizontal axis machine, and need an effective brake to avoid overspeed.
Vertical axis machines are cheaper to make and maintain, take up less space, and are safer for birds and bats. The vertical axis machines are easier to transport and install. They are less vulnerable to lighting strikes. They tend to be quieter because they turn more slowly. They are easier to work on, with generators, mill stones, pumps, or power takeoffs often at ground level. They are less dangerous for workers, but even simple machines are powerful and should be treated with care.
The problem with vertical axis rotors is that current designs are not as efficient as the horizontal axis machines, but they may be more cost effective. They can be placed close together with effects that increase speed and performance rather than requiring the wide spacing needed for many horizontal axis machines.
The Iranian Asbads with vertical blades
Iranian wind mills, known locally as asbads, were once widely used. These remarkable vertical axis wind machines are known from 644 CE. Vertical axis windmills built in Sistan (eastern Iran) for grain grinding and water pumping were also recorded by a Persian geographer in the ninth century. Asbads make use of the abundant free wind energy. The asbads are fixed in place so they are only suited for areas with a consistent wind direction. In some cases as many as forty windmills were built side by side to grind grain.
The wide and tall wall of the wind machines offered some protection to villagers from storms and blowing sand. To make the best use of the wind the mills were placed on the highest spots and no other construction was allowed to interfere with the wind flow. They accentuated the ridge lines.
The asbads could be built almost entirely from local and inexpensive materials. Reeds, planks or cloth covered vanes set in an opening in a mud wall capture the energy. The mud walls focus the airflow to turn the vanes. The cost would be primarily for labor, with the biggest cost for the millstones. During the windiest months the vanes in the wind catcher openings spin and rotate the millstones. Vertical axis Iranian wind machines were also used to pump water and chop sugar cane in other Islamic countries. The asbads made their way to China during the Mongol reign. They also spread to other territories.
Asbads can be seen in many Iranian towns but most are silent. They are still in use in Nashtifan N34° 25.933 E60° 10.527. The area around Nashtifan is known for its uniquely powerful winds from late May to late September. The name Nashtifan is derived from words that translate to “storm’s sting.” During the windy months the blades whirl with surprising velocity and turn the grindstones. Ali Muhammed Etebari, honored as a Living Human Treasure, maintains the asbads. Asbads that are abandoned can be identified where houses are being built in the wind fields.
The Chinese wind wheels
Mural paintings from the tombs of the late Eastern Han Dynasty (25–220 CE) at Sandaohao, Liaoyang City, include exquisite images of Chinese windmills. Wind wheel designs vary but there is a fixed frame on the outside, while the wind wheel rotates around the vertical axis in the center. Frames with sails provide the power. These machines can take advantage of the wind from all directions. A large transverse gear meshes with the vertical shaft gear connected to the sail. They are ideal for windy flat rural areas with few wind obstructions. The speed can be controlled by adjusting the sails (like a sailboat). A wind wheel tender adjusts the sails, just like for the large Dutch windmills.
In 1,000 CE, wind wheels were being used to pump irrigation water and to pump brine to make salt. F. H. King includes a photo of a wind wheel at the salt works at Chihli about 1900. The machine he looked at had a 4.5 meter span with eight sails totaling square 45 meters. The diameter of the vertical gear was 3 meters with 88 wooden teeth engaging a pinion of 15 leaves on the horizontal drive. Their use spread across much of China and they remained in use up to the 1950s and 1960s when they were displaced by electric pumps and mills.
The Future
The ingenious design of these vertical axis windmills still has much to teach us. Lessons from their use and performance can help the many companies now testing new designs around the world. Vertical axis machines can, and have been, integrated in building design. They can take advantage of enhanced wind speed around buildings and could be used to reduce turbulence and window damage.
In 1887 Prof James Blyth of Anderson’s College, Glasgow built what may have been the first vertical axis wind machine generating electricity. He used it for his cottage. It was a multi-scoop design, ten meters tall. Blyth offered to provide surplus electric power to the people of Marykirk for lighting the main street, but they turned him down because electric power was “the work of the devil.”
Research on vertical axis machines has continued and it is likely the efficiency will improve with more innovative designs. One reason for renewed interest is the potential use of vertical axis wind turbines in cities. They are better suited for urban environments where the wind flow and directions may be less predictable. These machines may take advantage of the sharp acceleration in wind around the corners of sharp building shapes. They are also a better choice for on-ground, building, and rooftop mounts in areas that would not allow installation of taller horizontal axis machines.
Wind remains one of the best and most sustainable energy sources. Global investment in wind machines is now billions of dollars a year. The 2025 Global Wind Report showed last year’s growth was 109 gigawatts (GW) of new onshore wind and 8 GW of offshore wind. This brings the global cumulative capacity of wind energy to 1,136 GW. In 2024, 55 countries installed wind turbines. Most of these are large tall horizontal axis machines that can cost a million dollars installed. For most of the world smaller wind machines must be low cost, made with simple materials, and easy to maintain. The ancient vertical axis designs from China and Iran may well be a solution or inspire a solution for these areas.
